How do I get past Giant Chasm?

When I go through the cave and get to the forest on the other side, I see a staircase on the top left and a path that is blocked off by trees and a ledge. How do I get to the staircase and what's up there?

Accepted Answer

there is a small drained pound in the forest, then the entire area frezzes and then the stairs are no longer blocked, then there is a cave enter it then you battle the legendary pokemon kyurem level 75, good luck, hope I helped